Best bet in a used IFR GPS?

Hi all,

Currently examining options for upgrading a 1979 172N with an IFR-certified
GPS. We currently have two good nav/coms, M-1 Loran, and ADF that we want to
replace.

Goal is to find the most cost-efficient IFR GPS install to replace the ADF
and add legal /G and DME capabilities. Keeping in mind that the plane is
worth maybe 50k we are not going to spend 10-12k on a GNS-430 class box, so
as I see it we have these options:

- Northstar M-3 Approach
- Garmin 155 or 155XL
- King KLN-89B or KLN-90B
- Apollo GX-50

AFAICT one can pick up a decent used example of any of these for between
$1500 and $3000 depending. I know we'll also need the annunciator and CDI,
and that installation/certification will comprise 50% of the total cost.

One of my big concerns in buying an older GPS is database updates. I want to
make sure we will not end up say a year or two down the road with an
expensive VFR GPS because updates are no longer available. Also, general
mfr. support.

I would like a decent moving-map capability, but given that we have none in
the plane right now, even a simple airspace depiction like the KLN-89B would
be a significant gain. If we want something snazzy we can get it better on a
handheld anyway. I would spend an extra $500 for a better map, but $1000 or
$1500 I'd wonder about.

What would you guys do?

Best,
-cwk.